1. Field of the Invention
The present invention relates to an electrostatic suction driving apparatus that is driven by electrostatic force, and more particularly to an electrostatic suction driving apparatus in which higher driving force can be generated through higher electrostatic force (Coulomb force).
2. Description of the Related Art
Prior art technical documents in associate with a conventional electrostatic suction driving apparatus can include, for example, Japanese Unexamined Patent Application Publication No. 2001-346385 or the like. FIG. 10 is a view illustrating a schematic block diagram of an electrostatic suction driving apparatus as shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2001-346385. FIG. 11 is a timing chart illustrating an electrical signal as shown in FIG. 2 of Japanese Unexamined Patent Application Publication No. 2001-346385.
In the electrostatic suction driving apparatus, a first stator 2a and a second stator 2b face each other in a state in which they are spaced apart at a predetermined distance, as shown in FIG. 10. A mover 3 for sliding to move is disposed between the first stator 2a and the second stator 2b. 
Three lines of electrodes A, B and C (a firs electrode) sequentially mounted on a predetermined direction are mounted on the first stator 2a. One line of an electrode D is mounted on the second stator 2b. The mover 3 further includes electrode portions 3a respectively disposed corresponding to electrode pitches of the electrodes A, B and C on one of surfaces of the first stator 2a, and a flat electrode portion 3d facing the second stator 2b on the other surface. Both of the electrode portions 3a and 3d form one line of an electrode E (a third electrode D) which is maintained under a voltage as same as that of the portions.
As shown in FIG. 11, electrostatic force (Coulomb force) that acts between the electrodes A and the electrode E causes the mover 3 to be sucked toward the first stator 2a, when a voltage is applied to the electrodes A disposed on the first stator 2a and a voltage on the electrodes A becomes higher than that of the electrode E disposed on the mover 3. In that case, a state where the electrodes A and the electrode portions 3a exactly overlap with each other is the most stable state, whereby force to the mover 3 is applied from the electrodes A so that the electrodes A and the electrode portions 3a overlap with each other. Then, the mover 3 is sucked toward the second stator 2b, when an electrode for applying a voltage is switched to the electrode D disposed in the second stator 2b. Further, force to the mover 3 is applied by the same mechanism as that at a time when a voltage is applied to the electrodes A from the electrode B such that the electrode B and the electrode portions 3a overlap with each other, when an electrode for applying a voltage is switched to the electrode B disposed in the stator 2a. A series of those operations, i.e., a voltage is sequentially applied from a voltage source 6 to the electrodes A→the electrode D→the electrode B→the electrode D→the electrode C→the electrode D→the electrode E, . . . , through a switching circuit 5 (while a voltage is alternately applied to the electrodes A to C disposed on the first stator 2a and the electrode D disposed in the second stator 2b, and at the same time the electrodes E disposed on the first stator 2a are sequentially switched in a predetermined direction). As described above, while the mover 3 vibrates up and down microscopically, it is driven in an arranged direction (the right side in the drawing) of the electrodes mounted on the first stator macroscopically.
In case that the aforementioned electrostatic suction driving apparatus is used as a driving apparatus for moving a lens for auto focusing with it mounted in a camera or the like. It is necessary to obtain driving force to a degree for moving the lens, and to increase the moving speed, the response speed or the like. To this end, there is a need for an electrostatic suction driving apparatus capable of obtaining high driving force by generating high electrostatic force (Coulomb force).
In this case, the electrostatic force has the property that it is proportional to the square of a voltage applied and areas facing each other on electrodes, but it is inversely proportional to the square of a gap size. It is therefore possible to obtain high electrostatic force by setting these factors as an optimal value.
There is, however, a limitation to an increased application voltage due to problems caused by a battery capable of being mounted in a camera, such as breakdown voltage, . . . . There is also a limitation to a narrowed gap size due to problems caused by accuracy in machining.
Moreover, the conventional electrostatic suction driving apparatus has a structure in which surface on respective electrodes E on the first and second stators 2a and 2, and surfaces on respective electrodes on the mover 3 face each other. For this reason, in order to widen the opposite area between the electrodes, it is necessary to increase the area on each of the electrodes disposed on the first stator 2a, the second stator 2b and the mover 3 in the aspect of their surfaces. In this case, however, the electrostatic suction driving apparatus itself becomes bulky. In addition, the weight of the mover 3 increases. This results in a lowered moving speed or a slow response speed of the mover 3.
An advantage of the invention is that it provides an electrostatic suction driving apparatus which can be compact and can generate high driving force.
As another problem, electrostatic suction force generated by the electrostatic suction driving apparatus is minute, whereby it is necessary to enhance the efficiency of electrostatic suction force generated needs. To this end, it is necessary to lower friction which may be generated in sliding between the mover and the stator as less as possible.
With Regard to this point of view, in the electrostatic suction driving apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2001-346385, a stopper 10 disposed on one of the stator 2a or the mover 3, and an area 8 disposed at opposite ends of the electrode E on the other one of the stator 2a or the mover 3 is designed to simply come in contact with each other to slide, as shown in FIGS. 14, 16 to 18 or the like. As described above, a part of electrostatic suction force is susceptible to loss due to friction heat or the like. This causes the driving efficiency of the mover not to be increased.
Another advantage of the invention is that it provides an electrostatic suction driving apparatus in which frictional resistance between a stator and a mover can be lowered to move the mover in a stable manner.
Moreover, in the conventional electrostatic suction driving apparatus, a static charge is generated in the first electrode on the first stator 2a when a relatively high voltage is applied to the first electrode (one of the electrodes A, B and C) on the first stator 2a, and a negative charge is thus induced in the third electrode (the electrode E) on the mover 3. In a similar manner, a static charge is generated in the second electrode of the second stator 2b when a relatively high voltage is applied to the second electrode (the electrode D) of the second stator 2b, and a negative charge is thus induced in the third electrode (the electrode E) of the mover 3.
As described above, the mover 3 is charged with a negative charge when a negative charge is kept induced in the third electrode (the electrode E) on the mover 3. Thus, in case that the mover 3 is not discharged, the movement of the mover 3 becomes slow. As described above, problems may be caused when the moving speed or the response speed is likely to be slow.
Japanese Unexamined Patent Application Publication No. 2001-346385 discloses that the electrode portions 3a disposed on one of surfaces of the mover 3 and the electrode portion 3d disposed on the other one of surface of the mover 3 are maintained as same voltages. FIG. 6 in Japanese Unexamined Patent Application Publication No. 2001-346385 shows that the electrode F disposed on the mover 3 is grounded. As described above, if all the electrode portions on the mover 3 are set as same voltages, i.e., the ground potential, the above described problems do not occur.
In Japanese Unexamined Patent Application Publication No. 2001-346385, however, in case that the mover 3 is formed of a conductor or material having a low resistance, it is likely that the first electrode on the first stator 2a and the second electrode on the second stator 2b may be shorted through the mover 3 when external force is applied to incline the mover 3. Therefore, in Japanese Unexamined Patent Application Publication No. 2001-346385, it is necessary to form the mover 3 as an insulator. For this reason, in order for the electrode portions 3a disposed on one of surfaces of the mover 3 and the electrode portion 3d disposed on the other one of surface of the mover 3 to have same voltages, dedicated pattern lines or the like for connecting the electrode portions 3a and the electrode portion 3b should be formed on the surface of the mover 3. Accordingly, a charge eliminating cable for connecting the movers 3 and the ground potential must be connected to the pattern lines, and the degree of freedom for connecting the charge eliminating cable to the mover 3 capable of being movable is likely to be limited. As a result, it is likely that the assembly of the entire device becomes difficult.
Meanwhile, the conventional electrostatic suction driving apparatus has a structure in which the mover 3 is sequentially driven in a direction in which the first electrodes mounted on the first stator 2a are arranged (a moving direction) macroscopically, while vibrating up and down microscopically.
That is, an amount of movement (displacement X) in a direction in which the mover 3 is arranged increases when the mover 3 moves upwardly in a direction in which it is sucked toward the first electrode, but decreases when the mover 3 moves downwardly in a direction in which it is sucked toward the second electrode. Therefore, the mover 3 moves upward and downward between the first stator 2a and the second stator 2b, whereby it is not smoothly driven.
Still another advantage of the invention is that it provides an electrostatic suction driving apparatus in which the degree of freedom for connection to a charge eliminating cable is increased to improve assembly of the apparatus.
Still another advantage of the invention is that it provides an electrostatic suction driving apparatus in which a mover is smoothly driven.